In recent years, along with a rising level of integration in semiconductor devices, circuit patterns of transistors and so on configuring these semiconductor devices are being increasingly miniaturized. Required in this miniaturization of the patterns is not simply a thinning of line width but also an improvement in dimensional accuracy and positioning accuracy of the patterns. This trend applies also to semiconductor memory devices.
Conventionally known and marketed semiconductor memory devices such as DRAM, SRAM, and flash memory each use a MOSFET as a memory cell. Consequently, there is required, accompanying the miniaturization of patterns, an improvement in dimensional accuracy at a rate exceeding a rate of the miniaturization. As a result, a large burden is placed also on the lithography technology for forming these patterns which is a factor contributing to a rise in product cost.
Furthermore, resistance varying memory is attracting attention as a candidate to succeed these kinds of semiconductor memory devices employing a MOSFET as a memory cell. The resistance varying memory herein includes phase change memory (PCRAM: Phase Change RAM), in addition to the resistance varying memory (ReRAM: Resistive RAM). The resistance varying memory uses a transition metal oxide as a recording layer to store a resistance state of the transition metal oxide in a non-volatile manner. The phase change memory uses chalcogenide or the like as a recording layer to utilize resistance information of a crystalline state (conductor) and an amorphous state (insulator).
Two kinds of variable resistors in the aforementioned resistance varying memory are known, namely a unipolar type and a bipolar type. In the case of bipolar type resistance varying memory, the variable resistor is applied with a voltage pulse (write pulse, erase pulse) of different polarity for a setting operation (write) and a resetting operation (erase). In the setting operation, the variable resistor shifts from a high-resistance state to a low-resistance state, and in the resetting operation, the variable resistor shifts from the low-resistance state to the high-resistance state.
On the other hand, in the case of unipolar type resistance varying memory, the variable resistor shifts to the high-resistance state or low-resistance state as a result of conditions such as amplitude and time of an applied voltage pulse. Accordingly, in the unipolar type, there occurs a phenomenon known as incorrect write where, during application of the erase pulse to the variable resistor, a write is performed again subsequent to erase being performed. Since most resistance varying memories actually capable of manufacture have unipolar characteristics as well as bipolar characteristics, the problem of incorrect write in these resistance varying memories remains unsolved.